Constant efficiency sound amplifier



Dec. 17, 1940. RUB|NSTE|N 2,224,931

CONSTANT EFFICIENCY SOUND AMPLIFIER Filed Nov. 26, 1938 ATTORNEY.

Patented Dec. 17, 1940 UNITED STATES PATENT OFFICE 1 Claim.

This invention relates to sound amplifying devices.

One object of the invention is to provide a device of the character described according to a 6 new and improved principle whereby the emciency curve of the sound amplifying device is relatively constant.

The provision of a mechanical sound amplifier having a uniform efficiency curve has long been sought for, the usual curve having a peak where the frequency happens to best harmonize with the vibratory characteristics of the horn or other sound amplifier. From that peak it has been observed that the curve dropped sharply on both sides, indicating a greatly lowered efliciency. As a consequence the tones have suffered distortion, often resulting in harsh or raucous notes which would have the effect of confusing the sounds and produce noise instead of clear music. With my invention, the eificiency curve is relatively uniform, the peak referred to being flattened down and the low points of the curve being substantially raised. The result is my amplifier will reproduce notes accurately over the entire musical scale and regardless of the volume of sound produced.

Another object of the invention is to provide a simple compact and durable amplifier, capable of attaining results which cannot be obtained electrically, as in a radio receiving unit.

Other objects and advantages of the invention will become apparent as the specification proceeds.

With the aforesaid objects in view, the inven- 5 tion consists in the novel combinations and arrangements of parts hereinafter described in their preferred embodiments, pointed out in the subjoined claim, and illustrated in the annexed drawing, wherein like parts are designated by the 40 same reference characters throughout the sev'- eral views.

In the drawing:

Figure 1 is a perspective isometric view with parts removed and in section showing a device 45 embodying the invention.

Fig. 2 is a horizontal sectional view of the de vice.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2.

50 Fig. 4 is a sectional view of the device, like that of Fig. 2, but showing a modification on a reduced scale.

The advantages of the invention as here outlined are best realized when all ofits features 55 and instrumentalities are combined in one and the same structure, but, useful devices may be produced embodying less than the whole.

It will be obvious to those skilled in the art to which the invention appertains, that the same may be incorporated in several difierent con- 5 s-tructions. The accompanying drawing, therefore, is submitted merely as showing the preferred exemplification of the invention.

Generally described, the invention includes a relatively nonvibrating sound distributing cham- 10 her, with relatively freely vibrating boards mounted in operative relation thereto. These boards or walls are desirably restrictedly responsive to the sound impulses through openings in the chamber walls. Preferably these vibratory 15 walls taper to accommodate different wave lengths, and desirably the walls are of different widths to accommodate diiierent ranges of wave lengths, so that a resonator results responsive to a particular range of sound wave frequency. In 20 conjunction with these walls, it is best to provide compartments for transmission of sound waves to the respective vibratory walls according to their individual ranges. For the very short wave lengths, the speaker unit or sound source pref- 5 erably directly communicate with the vibratory walls at their narrowest regions.

Referring in detail to the drawing, Ill denotes the invention. The same may include a chamber H formed by side walls II, II and an end wall 30 I4. All of these walls consist of a material or are so constructed as to be relatively unresponsive to sound waves. The chamber II is relatively closed except for the end opening l5 and the lateral openings such as ll, whereby the chamher constitutes a sound conduit or distributing chamber. Regarded as such. it will be apparent that the chamber ll may be made of any suitable size and shape, for example, it may be arranged to taper toward the end opening I5. 40

' Responsive to the sound waves from the chamber I l are one or more compartments or elements such as the vibratable boards or walls II, II. Desirably the same may be tapered with their narrower end portions adjacent to the chamber end opening 15. Where a plurality or a series of walls ll, [8 are used, two or more may be of substantially different widths, so that each accommodates a diflerent'range of sound waves. The walls l1, I! may be variously mounted. For instance, bridge pieces I! interconnect the chamber II with the walls. such as the walls ll and desirably form compartments 20, 2| between the chamber and the adjoining walls ll,- II. It will be noted that the bridge Pieces. ll may be integral extensions of the chamber walls l2, and that preferably, where the walls [1, l8 are marginally interconnecteed as at 22, the bridge pieces extend to points spaced from the comers 22. This has a double purpose, since it results in that the compartments 20 are of substantially greater width than the compartments 2|, and permits greater freedom of vibration of the walls l1, l8, particularly the former which are thus substantially wider than the operative parts of the walls l8.

It will be observed that the openings may in.- crease in width downward to conform to the character of the sounding walls I1, N. The latter may desirably be spaced from the wall' I at their lower edges 23, the latter and the upper edges 24 being preferably free.

For supporting a sound source 25, such as a diaphragm or magnetic unit or other device,

in spaced relation to the chamber end opening IS, the bridge pieces I9 desirablyextend above the end opening l5, and the upper end portions of the vibratory Walls I1, l8 similarly extend above the end opening I5, with the unit 25 adapted to seat on the extensions 26 of the bridge pieces. For instance, the latter may be rabbeted as at 21 for this purpose. Thus the unit 25 may transmit its full sound strength'to the chamber H, and yet permit high frequency waves to travel directly to the upper portions of the vibratory walls I1, l8. In order that the edges 28/of the opening l5 shall not impede the sound waves, these edges 28 are preferably beveled off as shown.

In operation, the sound waves from the sound source ,25 travel straight ahead into the relatively nonvibrating second distributing chamber II from which they aredistributed through the openings I 6 to the vibratable walls or elements ll, I8 as at the open ended compartments 20, 2|. The arrangement is such that the longest sound waves'are transmitted to the lowest portions of vibratory elements, the progressively shorter sound waves operating at correspondingly higher, that is, narrower points of these elements. Thus the elements [9 are responsive to a range of sound waves longer than at least part of the range to which'the elements l8 are responsive. If desired, the elements I 8 may terminate above the bottom edges of the elements IT. The very short frequency notes, pass laterally above the edges 28 directly to the adjacent narrow areas of the elements l1, l8. Thus the amplifier works with equal efiiciency for all sound waves, since that certain parts of the device In may be de- 5 sirably tensioned. For example, the device 30 may have walls such as l3, l1 and I8, except that walls l2a terminate at a wall l3, and bridge pieces 3| are provided in place of the adjacent elements l9. These bridge pieces 3| are securely 10 connected to the wall l8 but are spaced from the adjacent wall I3, to permit intermediate tensioning thumb screws -32 of the right-hand, left-hand type to interconnect the elements He and 3|. Accordingly, adjustment of the screws 15 32 may cause a tensioning or an expansion force to be exerted on the walls l1, l8 relative to thewalls l2a, I3 to produce desired tonal qualities.

I Claim: 1 J

A device for amplifying sound received from 20 a loud speaker unit, including a first member having side walls providing a tapered chamber, said member having an end wall connected to the side walls and forming a complete closure for the chamber at the large end thereof, a 25 second member having a tapered passage therein receiving the first'member so that both members taper in the same direction, the sidewalls of'the first member being spaced inwardly of the side walls of the second member to thus af- 30 ford'sound passages therebetween, the side walls of the first member having openings elongated in the direction of the taper and communicating with the last mentioned passages so that vibrations can enter the latter through said openings,

all the walls of the first member being constructed of a material that-is adapted to absorb sound vibrations so as to be relatively incapable of being vibrated by sound vibrations, the walls of the second members being vibrationally respon- 40 sive to said sound vibrations transmitted thereto through said openings, means interconnecting'the-members to support the second member with the ends thereof being free, the second member having atits small end a portion constituting a continuation of the first mentioned passage and-alined therewith and extending beyond the adjacent end of the first member, and a loud speaker unit mounted in said portion and facing into the first member, and the latter having-its adjacent end edges free and spaced inward of the said unit.

SAMUEL RUBINS'IEIN. 

